Method of preparing and maturing alkali cellulose



June 25, 1935. F, $TE|MM|G 2,005,811

METHOD OF PREPARING AND MATURING ALKALI CELLULOSE Filed Feb. 23, 1935Patented Jene 25, 1935 f PATNT OFFICE METHOD F PREPARING AND MATURINGALKALI (JELLULOSEV Franz Steimmig, Hermsdorf, near Kynast,

Germany Application February 23, 1933, Serial No. 658,132

In Germany 2 Claims.

My invention relates to an improved method of preparing and ripening ofalkali cellulose for the production of viscose.

With the methods hitherto known sheets or. slates of cellulose aresubjected in vats to 'the action of an alkali solution of about 18% forseveral hours, whereupon they are freed by pressure from the excess oflye and are comminuted during several hours. The succeeding maturingprocess takes place in large receptacles of sheet iron at a temperatureof to 24 C. and lasts two to four days.

'I'hese known methods require a great lot of long lasting operations,much power, and big and expensive apparatus. Then again the single stepsof the process which are continued at intervals must be carefullywatched and the attendants are exposed to the unhealthy effects of theused materials.

Now I do away with these inconveniences by using a continuous thin stripor web of cellulose which is successively conveyed in a continuousoperation through the mercerizing lye, is freed from the excess of lyeby pressing rollers, and is led through the ripening room. By thesemeans the whole process is simplified, cheapened and improved.

An important feature of my invention consists in the use of a roll ofpaper or of paper board instead of sheets or slates. The web of such aroll, which may be previously dried, is conveyed by a suitabletransporting support, for instance by a wire net preferably of astainless material, through the lye bath of the usual concentration ofabout 18% NaOH. This bath is contained in an iron vat and suitablerollers keep the wire net and the cellulose band underneath the level ofthe liquid.

The mercerizing effect begins as the cellulose 4o web enters into thelye and is nished in a comparativelylshort time inasmuch as thecellulose is introduced in the form of a thin layer. It is deemedsuperiluous to give exact numbers for the time needed for themercerization as this depends upon the thickness and the density of thecellulose web. But it may be pointed out that the velocity of thetransport of the web and the length of the Vat are to be chosen withrelation to the thickness of the web of the cellulose. Under normalconditions a length of the vat of 10 to 12 meters and a conveyingvelocity of one meter in a minute will sufllce. But I wish it to beunderstood that I do not conne my invention by these gures.

Instead of one conveying band for carrying the March '1, 1932 (C1.26o-1o) between which the cellulose strip is inserted. With a high vatit is possible to lead therein the cellulose strip in a zigzag path, sothat the vat may then be shorter. It is also possible'to convey two ormore cellulose layers one above the other through the vat.

At the exit end of wthe vat there are arranged two or more squeezingrollers, between which the cellulose web reposing upon the conveyer isintroduced for pressing out the excess of lye. The distance of thepressing rollers or the pressure to be exerted upon the material oughtto be adjustable in order to be able to denne the amount of alkaliremaining in the cellulose and to obtain the usual relation of 1 :2.

After leaving the pressure device the squeezed layer of alkali celluloseis removed from the conveying support and is led by means of a secondconveyer into the ripening room, while the rst conveyer returns to theentrancev side to receive a fresh cellulose and to so repeatcontinuously its operation.

In the case that the alkali cellulose in leaving the pressing deviceshould adhere' to the squeezing rolls a scraper may be provided forwiping off of the cellulose. One roll or more lof the pressure devicemay be covered with rubber or any other material suitable for carryingout the work to be done. In some c ases two or more pressing devices maybe arranged one behind the other.

If it is desired to fully remove the hemi cellulose from the cellulosetreated with the lye this may be in an eflicient manner obtained by thepresent invention. To this end it is only necessary to lead thecellulose band through two or more baths of lye. Between the singlebaths the excess of lye can be removed from the cellulose and the timeof the passage of the single bath which may be of diierentconcentrations can'accordingly be abbreviated. It is also possible toadd to the bath some substances as for instance hydrochinon or molassesadapted to iniluence the mercerizing effect. Means are also to beprovided for supplying fresh lye.

After the alkali cellulose band has left the pressing device themercerizing process is nished and the product obtained is now to besubjected to the ripening process. To this end the alkali cellulose bandleaving the pressing device is led on to a second conveyer which forinstance may consist 0f a suitable cotton material. By means of thisconveyer the cellulose band is brought through a slot into the heatingreceptacle, wherein the ripening is obtained. The receptacle has atemperature higher than 30. It is special advantage of this part of theinvention that the alkali cellulose owing to the form of a thin layer isripened in a much shorter time at a certain temperature than with theusual methods. The known methods can be carried out at a low temperatureonly as the alkali cellulose has the form of quite irregular pieces. Theripening lasts therefore longer because the temperature used dependsupon whether the mass treated can be rapidly and with certainty cooledat/the right moment for interrupting the ripening. With the knownmethods it is very diftlcult to act accordingly owing to the irregularform of the mass treated. On the other hand this is easily carried outwith the new method because the layer of alkali cellulose is thin and ofan equal thickness. As it is possi le to cool speedily the thin layer ofcellulose by ringing it into a cooling zone and to so prevent aprogressive ripening, I am able to use a higher ripening temperature. Ofcourse the timeof passing the material through the ripening room and thetemperature used must yagree with the desired degree of ripeningdesired.

To prevent an undesirable drying of the alkali cellulose the air withinthe ripening room can be conditioned with humidity, for instance byblowing into it steam from a boiler.

During the whole operation the alkali cellulose can be protected againstthe carbonio acid contained in the air by appropriately enclosing thewhole apparatus or by circulating fresh air through the shop.

summarizing I may say that the above process aifords the advantages of'a continuous economical working on the least space and with the leastliability of any harm to the attendants. Moreover the new process allowsto vary its different steps and to adapt them to the quality of the usedprimary materials.

In the accompanying drawing I have' diagrammatically illustrated themode of carrying out the new process. v

I1 is a shaft or any other support for the supply roll I of thecellulose band 2 which'ls unwound and led between the rolls 3 and 4 intothe' alkali lye contained in the vat 5. The cellulose band is carried bythe endless conveyer 6 and the cooperating rolls 1, 8, 9 and I0 throughthe bath between the squeezing rolls, I I, I2. After leaving thesqueezing rolls the conveyer 6 returns into the vat giving oiI thecellulose band to the second conveyer I3 which brings it into theripening cabinet Il. Here the cellulose band is successively taken holdof by a series of horizontal endless conveyers Ilia, lib, Ic etc.arranged one above the other. The cellulose band thus leaves theripening cabinet Il at the exit I6 for the cool-N ing zone outside ofthe cabinet. But the cooling zone may be arranged within the cabinet.

For the sake of clearness I have indicated the conveyers by dotted linesand the cellulose band by dash and dot lines.

What I claim is:

1. A'method of preparing and maturing alkali cellulose for theproduction of viscose, comprising the use of a roll of a thin strip orweb of cellulose, unwinding this continuous strip from the roll andintroducing it into the mercerizing lye, freeing it at the exit from thelye from the excess of lye by squeezing rolls, leading it into andthrough an enclosed, uniformly heated atmosphere to ripen the same, andcontrolling therein the degree of moisture.

2. A method of preparing and maturing alkali cellulose for theproduction of viscose, comprising I the use of a roll of thin striporweb of cellulose, unwinding this continuous strip from the roll andintroducing it into the mercerizing lye, freeing it at the exit from thelye from the excess of lye by squeezing rolls, leading it into andthrough a ripening room. heated to a temperature higher than 30 C. andcontrolled with regard to the degree of moisture and then into a coolingzone.

` FRANZ STEIMMIG.'

